Ashton Moss is a mixed use commercial and leisure development situated off J23 of the M60 near Manchester. The development covers 64 hectares and provides over 1M sq ft of commercial, retail, and industrial space, along with a further 175,000 sq ft of leisure and green open space.
The Challenge
This large development needed to be completed very quickly to make the development financially viable. The site was a “mountain of pre-tipped inert waste” of very variable specification Construction, Demolition and Excavation Waste (CDEW) that had been stockpiled on a partially excavated and backfilled site, including areas of natural peat. It was constrained by the nearby M60, A635 and Ashton North Bypass.
The area was made up of peat and alluvial clays. Surprisingly, the stockpiled material was usable from a geotechnical and contamination point of view, but was too wet (23% moisture content) to compact adequately to meet specification requirements that limited settlement to 25mm within 6 months.
The tight construction timescale meant traditional surcharging was impractical and double handling of the material would have resulted in a massive increase in costs. To meet program, the 700,000m³ earthworks had to be completed over the winter with high expected rainfall.
The Solution
A layer of Fildrain drainage geocomposite was placed for every 1m of fill. Using Fildrain 7DD reduced the consolidation period by as much as 80%, with the specified settlement complete within 4 weeks. The double cuspated drainage core drains from both sides, while also providing an impermeable barrier that allows vertical migration of pore water, but seals against rainfall ingress.
Fildrain 7DD drainage geocomposite is easy to install, avoiding all the difficulties of placing layers of expensive gravel. It was observed that the lower layers were draining effectively even before the upper layers were placed – consolidation starts immediately as soon as the Fildrain is placed.
ABG Fildrain in layers draining embankment
The ABG Service
ABG provided full technical support to propose and gain approval from the various authorities for the use of Fildrain 7DD drainage geocomposite. Deliveries were coordinated to fit the work schedule to avoid stockpiling on a tight site.
This scheme is an example of implementing an idea from the Highways England “Managing Down Costs” Toolkit.
(ref:Published paper “Advanced engineering solutions using geocomposite drainage for fast consolidation in compacted fill Robinson,N. et al. EuroGeo6 Sept 2016)
Contact ABG today to discuss your embankment drainage or earth consolidation project’s specific requirements and discover how ABG past experience and innovative products can help.
